/*
 * Copyright 2008 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.zxing.oned;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.NotFoundException;
import com.google.zxing.common.BitArray;

/**
 * <p>Implements decoding of the EAN-13 format.</p>
 *
 * @author dswitkin@google.com (Daniel Switkin)
 * @author Sean Owen
 * @author alasdair@google.com (Alasdair Mackintosh)
 */
public final class EAN13Reader extends UPCEANReader {

    // For an EAN-13 barcode, the first digit is represented by the parities used
    // to encode the next six digits, according to the table below. For example,
    // if the barcode is 5 123456 789012 then the value of the first digit is
    // signified by using odd for '1', even for '2', even for '3', odd for '4',
    // odd for '5', and even for '6'. See http://en.wikipedia.org/wiki/EAN-13
    //
    //                Parity of next 6 digits
    //    Digit   0     1     2     3     4     5
    //       0    Odd   Odd   Odd   Odd   Odd   Odd
    //       1    Odd   Odd   Even  Odd   Even  Even
    //       2    Odd   Odd   Even  Even  Odd   Even
    //       3    Odd   Odd   Even  Even  Even  Odd
    //       4    Odd   Even  Odd   Odd   Even  Even
    //       5    Odd   Even  Even  Odd   Odd   Even
    //       6    Odd   Even  Even  Even  Odd   Odd
    //       7    Odd   Even  Odd   Even  Odd   Even
    //       8    Odd   Even  Odd   Even  Even  Odd
    //       9    Odd   Even  Even  Odd   Even  Odd
    //
    // Note that the encoding for '0' uses the same parity as a UPC barcode. Hence
    // a UPC barcode can be converted to an EAN-13 barcode by prepending a 0.
    //
    // The encoding is represented by the following array, which is a bit pattern
    // using Odd = 0 and Even = 1. For example, 5 is represented by:
    //
    //              Odd Even Even Odd Odd Even
    // in binary:
    //                0    1    1   0   0    1   == 0x19
    //
    static final int[] FIRST_DIGIT_ENCODINGS = {
            0x00, 0x0B, 0x0D, 0xE, 0x13, 0x19, 0x1C, 0x15, 0x16, 0x1A
    };

    private final int[] decodeMiddleCounters;

    public EAN13Reader() {
        decodeMiddleCounters = new int[4];
    }

    @Override
    protected int decodeMiddle(BitArray row,
                               int[] startRange,
                               StringBuilder resultString) throws NotFoundException {
        int[] counters = decodeMiddleCounters;
        counters[0] = 0;
        counters[1] = 0;
        counters[2] = 0;
        counters[3] = 0;
        int end = row.getSize();
        int rowOffset = startRange[1];

        int lgPatternFound = 0;

        for (int x = 0; x < 6 && rowOffset < end; x++) {
            int bestMatch = decodeDigit(row, counters, rowOffset, L_AND_G_PATTERNS);
            resultString.append((char) ('0' + bestMatch % 10));
            for (int counter : counters) {
                rowOffset += counter;
            }
            if (bestMatch >= 10) {
                lgPatternFound |= 1 << (5 - x);
            }
        }

        determineFirstDigit(resultString, lgPatternFound);

        int[] middleRange = findGuardPattern(row, rowOffset, true, MIDDLE_PATTERN);
        rowOffset = middleRange[1];

        for (int x = 0; x < 6 && rowOffset < end; x++) {
            int bestMatch = decodeDigit(row, counters, rowOffset, L_PATTERNS);
            resultString.append((char) ('0' + bestMatch));
            for (int counter : counters) {
                rowOffset += counter;
            }
        }

        return rowOffset;
    }

    @Override
    BarcodeFormat getBarcodeFormat() {
        return BarcodeFormat.EAN_13;
    }

    /**
     * Based on pattern of odd-even ('L' and 'G') patterns used to encoded the explicitly-encoded
     * digits in a barcode, determines the implicitly encoded first digit and adds it to the
     * result string.
     *
     * @param resultString string to insert decoded first digit into
     * @param lgPatternFound int whose bits indicates the pattern of odd/even L/G patterns used to
     *  encode digits
     * @throws NotFoundException if first digit cannot be determined
     */
    private static void determineFirstDigit(StringBuilder resultString, int lgPatternFound)
            throws NotFoundException {
        for (int d = 0; d < 10; d++) {
            if (lgPatternFound == FIRST_DIGIT_ENCODINGS[d]) {
                resultString.insert(0, (char) ('0' + d));
                return;
            }
        }
        throw NotFoundException.getNotFoundInstance();
    }

}
